1. Technical Field
The present invention relates to a roller that transports a medium such as a paper sheet, and a printing apparatus including the roller.
2. Related Art
As this type of printing apparatus, there is known an ink jet printer that performs printing on a medium such as a paper sheet by ejecting liquid such as ink onto the medium that is being transported by transport rollers. As an example of this type of printer, there is provided a printer having spurs that nip and transport a medium subjected to printing (see, for example, JP-A-2006-347119). The spur of JP-A-2006-347119 is formed of a circular metal sheet (wheel) that has a plurality of tooth tips, and a molded member (holder) that is molded integrally with the metal sheet and supports the metal sheet in a rotatable manner. Two spurs are provided so as to be adjacent to each other in a width direction of the medium that intersects a transport direction of the medium. The spurs as described above transport the medium in such a manner that the tooth tips of the metal sheets are brought into contact with the medium. With this operation, the contact area between the medium and the spurs is reduced, thereby suppressing transfer of ink from the medium.
In the spur of JP-A-2006-347119, the metal sheet (wheel) is formed by press working, and hence the metal sheet is formed by cutting off tie-bar portions that couple a base material and the metal sheet to each other. Therefore, tie-bar cut portions (cut portions) are formed on the outer periphery of the metal sheet in addition to the tooth tips. The shape of the tie-bar cut portion is different from the shape of the tooth tip and is formed on a radially inner side of the metal sheet with respect to the tooth tip. Therefore, when the number of teeth of the metal sheet increases, an imaginary circle formed by connecting the tooth tips of the metal sheet into a circle differs from a perfect circle because the tooth cannot be formed at a portion where the tie-bar cut portion is formed. When the spurs are viewed in an axial direction (width direction of the medium) orthogonal to the side surfaces of the metal sheets thereof, if the tie-bar cut portions of the metal sheets adjacent to each other in the axial direction overlap each other or are distributed unevenly in a circumferential direction of the spurs, the shapes of the spurs differ from a perfect circle. As a result, the transport accuracy of the medium to be transported by the spurs may be decreased.
This problem may arise not only in the spurs described in JP-A-2006-347119 but also in rollers that transport a medium by metal sheets (wheels) having tie-bar cut portions.